As is known, a pump generally includes a pump body which defines a pump chamber usually positioned between an input valve and an output valve. In order to dispense the product contained in the pump chamber, the user actuates an actuating rod connected to a piston which slides in the pump body which generally causes the displacement of a second piston, called the low piston and which slides in a portion of the pump body with a reduced diameter until the output valve opens which causes the product contained in the pump chamber to be expelled under pressure. When the user lets go and the actuating rod moves back up to its rest position, under the action of a return spring, some product is sucked into the inside of the pump chamber through said input valve.
The object of the present invention is to overcome certain drawbacks which arise with the type of pump.
Thus, a drawback arises due to the relatively large dead space which exists upstream from the input valve of the pump chamber, in the flow direction of the product. Indeed, the plunger tube generally opens into the bottom of the pump body, so that this entire portion of the pump body which is located below the low piston and the input valve, is filled with product. This has the effect of inducing a non-negligible back pressure which makes the complete emptying of the tank difficult.
One of the objects of the present invention is to reduce the dead spaces and the back pressure of the pump.
The object of the present invention is also to improve priming of this type of pump, the latter generally requiring three or four actuation jolts of the pump before obtaining a completely filled pump chamber.
The object of the present invention is also to reduce the number of priming jolts required for priming the pump.
On the other hand, the return spring of the pump is generally mounted between the bottom of the pump bottom and the seat of the input valve which is floatably mounted inside said pump body. The spring is therefore in contact with the product, this may cause a certain number of problems when said spring is metal, as is often the case. The documents U.S. Pat. No. 4,511,069, FR-1 486 392 and DE-28 38 613 disclose such devices.
Another object of the present invention is to suppress any contact between the return spring of the pump and the product to be dispensed.